This invention relates to the field of multiple electrical connectors and mounting blocks therefor. More particularly, this invention relates to a new and improved mounting block and associated electrical terminal which is particularly useful as a telecommunications connector block.
Solderless multiple connectors have found applicability in many fields, particularly in the field of telecommunications equipment. These connectors may be used to establish interconnections between small diameter, insulated conductors in confined spaces where the use of screw type terminal strips or similar connecting devices are not suitable. In addition, some of these prior art connectors strip away the insulation from conductors inserted therein. These terminals incorporate an insulation displacement connector (IDC) portion.
The present invention relates to a connecting block and terminal wherein the connecting block comprises a retainer base for receiving a plurality of terminals and a cover which is snapped onto the base for retaining the terminals in precise orientations. Prior art examples of this general type of connecting block and terminal are found in U.S. Pat. Nos. 4,547,034 and 4,615,576. It will be appreciated that while connecting blocks and terminals of this type are in prevalent use, there continues to be a need for improvements to both the block and terminal design. Specifically, there is a need for improvements to the latch mechanism which provides attachment between the connecting block and mounting bracket. There is also a need for an improved IDC terminal configuration. Presently, there are at least four types of terminals used in teleconnections blocks including:
1. Simple "tuning fork" design PA1 2. Cylindrical "barrel" design PA1 3. "Looped wire" design PA1 4. Inclined "tuning fork" design
The simple tuning fork design, which is best described as two parallel beams sharing an integral base and defining, between them, a slot for the termination of insulated or bare wire, is the most common of all IDC contact designs. One limiting aspect of this contact type is that, as wire is terminated, the pivoting of the beams results in a tapered slot which leads to complications when terminating stranded wire due to the difficulty of keeping the wire strands in a coherent group. After termination, the slot taper also provides an uneven space for movement of individual strands which may lead to intermittent electrical connections. Another drawback to the straight tuning fork type is that, inherent to its design, are high stress gradients at the base of the slotted portion and along the beam elements, which limit the range of compatible wire gages and choice of material type to expensive, high strength alloys to avoid the onset of inelastic material yield which may degrade electrical performance. Examples of that type of IDC contact are the well known "66" terminal such as is described in U.S. Pat. No. 4,150,867, and tribeam types which are shown in U.S. Pat. No. 4,468,079.
The so called "barrel" design (which is disclosed, for example in U.S. Pat. No. 4,671,595), is comprised of a cylindrical conductor with a lengthwise slit for receiving insulated or bare wire. Unlike the simple tuning fork, this IDC type will maintain a parallel wire termination slot making it compatible with stranded wire. Also, because stresses are more evenly distributed, it is more resilient and therefore more compatible with a wide range of wire gauges and material types. The drawback of this design is that it does not permit applications where wire may be continuously looped from contact to contact. In essence, the inside of the barrel is a dead-end that prohibits the termination of wire without cutting or access to its end.
The looped wire IDC, which is disclosed, for example, in U.S. Pat. No. 4,381,880, combines the even stress distribution and parallel slot advantages of the barrel with the versatility of the straight tuning fork design. Its construction essentially consists of long cylindrical beams that are constrained at both ends such that a wire inserted between them will result in a bowing flexure which is optimal for the termination of both solid and stranded wire and for the termination of multiple wires in a single slot. The disadvantage of this contact type is that, while in manufacturing it results in virtually no process scrap, it is made by a wire forming operation which is slow and costly compared to progressive metal stamping operations used for other designs.
The inclined tuning fork IDC type makes use of a contact of the general tuning fork shape, but varied in such a way that the beam elements are thin, wide blades that are oriented and supported in a plastic housing at an angle of approximately 45.degree. with respect to the axial orientation of the wire to be terminated. Examples of this type of terminal are disclosed in the aforementioned U.S. Pat. Nos. 4,547,034 and 4,615,576. As the wire is inserted, the inclination of the contact forces the blades to rotate in a torsional respect, thereby resulting in the desired parallel slot and reduced stress concentration compared to the straight tuning fork design. The limitations of this IDC type are that, while the plastic support along the outside edges of the contact allow the opposing sides to rotate, they do not induce planar flexure of the blades that will result in the preferred bowing of the wire termination slot and the further distribution/reduction of material stress.
Also, to overcome the natural tendency of the wire to balance these torsional forces by assuming an orientation perpendicular to the contact, wire restraints are required on both the entry and exit sides of the contact. In most applications, wire strain relief is desired, but the requirement of having two distinct and separate strain relief features per terminal is more restrictive than other designs which use strain relief, but not as an integral and required aspect of the wire electrical connection.
While the four IDC types discussed above represent the vast majority of wire termination systems used in telecommunications networks today, it will be appreciated that, other prior art IDC contact designs presently in use are wrought with similar limitations in construction and performance.